Phonon scattering by nanostructures and point defects has become the primary strategy for minimizing the lattice thermal conductivity (κL) in thermoelectric materials. However, these scatterers are ...only effective at the extremes of the phonon spectrum. Recently, it has been demonstrated that dislocations are effective at scattering the remaining mid‐frequency phonons as well. In this work, by varying the concentration of Na in Pb0.97Eu0.03Te, it has been determined that the dominant microstructural features are point defects, lattice dislocations, and nanostructure interfaces. This study reveals that dense lattice dislocations (≈4 × 1012 cm−2) are particularly effective at reducing κL. When the dislocation concentration is maximized, one of the lowest κL values reported for PbTe is achieved. Furthermore, due to the band convergence of the alloyed 3% mol. EuTe the electronic performance is enhanced, and a high thermoelectric figure of merit, zT, of ≈2.2 is achieved. This work not only demonstrates the effectiveness of dense lattice dislocations as a means of lowering κL, but also the importance of engineering both thermal and electronic transport simultaneously when designing high‐performance thermoelectrics.
Eu‐doping effectively converges the valence bands of PbTe, while Na‐doping enables dense lattice dislocations, leading to an extremely low lattice thermal conductivity (κL) of <0.4 W m−1 K−1. This contributes to a high zT of ≈2.2, opening new possibilities for advancing thermoelectrics through dislocation and band‐engineering approaches.
A haloscope of the QUAX– a γ experiment composed of an oxygen-free high thermal conductivity-Cu cavity inside an 8.1 T magnet and cooled to ∼ 200 mK is put in operation for the search of galactic ...axion with mass ma ≃ 43 μ eV . The power emitted by the resonant cavity is amplified with a Josephson parametric amplifier whose noise fluctuations are at the standard quantum limit. With the data collected in about 1 h at the cavity frequency νc = 10.40176 GHz , the experiment reaches the sensitivity necessary for the detection of galactic QCD-axion, setting the 90% confidence level limit to the axion-photon coupling gaγγ < 0.766 × 10−13 GeV−1.
The coupled transport properties required to create an efficient thermoelectric material necessitates a thorough understanding of the relationship between the chemistry and physics in a solid. We ...approach thermoelectric material design using the chemical intuition provided by molecular orbital diagrams, tight binding theory, and a classic understanding of bond strength. Concepts such as electronegativity, band width, orbital overlap, bond energy, and bond length are used to explain trends in electronic properties such as the magnitude and temperature dependence of band gap, carrier effective mass, and band degeneracy and convergence. The lattice thermal conductivity is discussed in relation to the crystal structure and bond strength, with emphasis on the importance of bond length. We provide an overview of how symmetry and bonding strength affect electron and phonon transport in solids, and how altering these properties may be used in strategies to improve thermoelectric performance.
Bonding interactions in thermoelectrics: Chemical bonding concepts and molecular orbital theory are used to understand electronic structures and the electronic and thermal transport in semiconductors. Emphasis is placed on the influence of local bonding interactions, such as bond length and orbital overlap, coordination environment, and the expression of lone‐pairs.
This work reported that waxes are a big source for the latent heat storage as phase change materials but they suffer from the weakness in their thermal conductivity so different types of additives ...are needed to enhance their thermal conductivity. A sort of Paraffin Wax (PW) and Microcrystalline Wax (MW) composites with different loading levels (0.5, 1 and 2wt%) of α Nano Alumina were successfully synthesized as Phase Change Materials (PCM). The resultant composite samples were characterized by Polarized Optical Microscope (POM), Deferential Scanning Calorimetric (DSC), X-ray diffraction (XRD) besides studying the Thermal Conductivity to investigate their homogeneity and heat storage capability. Data revealed that PW composites, with increasing the loading levels, have better thermal conductivity and latent heat than MW composites.
•Shape-stable and high-thermal conductivity c-PCMs composed of PEG and BPC are investigated.•Biological porous carbon materials not only shape PEG but also improve the thermal conductivity.•The ...maximum absorption of PEG reaches 85.36wt% without leakage in the PEG/BPC c-PCMs.•PEG/BPC c-PCMs show good thermal reliability even go through a 200 thermal cycles.
Shape-stable and high-thermal conductivity composite phase change materials (c-PCMs) composed of polyethylene glycol (PEG) and biological porous carbon (BPC) are investigated. BPC based on potatoes and white radishes are obtained by the carbonization method. The thermal conductivity of the BPC increases with the rising of the carbonization temperature due to the higher graphitization degree. Especially, BPC calcined at 1300°C for 2h resulted in the optimum PEG supporting matrix candidate, showing an attractive honeycomb-like microstructure. Calcination above 1300°C results in the destruction of the shape. BPC/PEG c-PCMs are synthesized via a vacuum impregnation approach. PEG equally distributed in the matrix material with a mass fraction of 85.36% approximately and it could keep its morphological stability after heating at 80°C for 40h. Moreover, the highest thermal conductivity is 4.5W/mK, which is about 10 times higher than the pristine PEG. Furthermore, no chemical interaction is found between the PEG and BPC. The melting and solidifying temperature, and enthalpy not vary upon a 200 thermal cycles test. This confirms the excellent chemical and structure stability for c-PCMs, which are within the most promising materials in the area of building heat preservation by being clean, energy-saving and recycled materials.
Abstract
Lattice thermal conductivity (κL) is one of the most fundamental properties of solids. The acoustic–elastic-wave assumption, proposed by Debye (Debye P. Ann Phys 1912; 344: 789–839), has led ...to linear phonon dispersion being the most common approximation for understanding phonon transport over the past century. Such an assumption does not take into account the effect of a periodic boundary condition on the phonon dispersion, originating from the nature of periodicity on atomic arrangements. Driven by modern demands on the thermal functionality of materials, with κL ranging from ultra-low to ultra-high, any deviation from the Debye approximation in real materials becomes more and more significant. This work takes into account the periodic boundary condition, and therefore rationalizes the phonon dispersion to be more realistic. This significantly improves the precision for quickly predicting κL without any fitting parameters, as demonstrated in hundreds of materials, and offers a theoretical basis rationalizing κL to be lower than the minimum currently accepted based on the Debye dispersion. This work paves the way for designing solids with expected κL and particularly inspires the advancement of low-κL materials for thermal energy applications.
Abstract
To develop high-performance thermoelectric devices that can be created using printing technology, the interface of a composite material composed of MASnI
3
and Bi
2
Te
3
, which individually ...show excellent thermoelectric performance, was studied based on first-principles calculations. The structural stability, electronic state, and interfacial thermal conductance of the interface between Bi
2
Te
3
and MASnI
3
were evaluated. Among the interface structure models, we found stable interface structures and revealed their specific electronic states. Around the Fermi energy, the interface structures with Te
II
and Bi terminations exhibited interface levels attributed to the overlapping electron densities for Bi
2
Te
3
and MASnI
3
at the interface. Calculation of the interfacial thermal conductance using the diffuse mismatch model suggested that construction of the interface between Bi
2
Te
3
and MASnI
3
could reduce the thermal conductivity. The obtained value was similar to the experimental value for the inorganic/organic interface.
Highly thermal conductivity materials with excellent electromagnetic interference shielding and Joule heating performances are ideal for thermal management in the next generation of communication ...industry, artificial intelligence and wearable electronics. In this work, silver nanowires (AgNWs) are prepared using silver nitrate as the silver source and ethylene glycol as the solvent and reducing agent, and boron nitride (BN) is performed to prepare BN nanosheets (BNNS) with the help of isopropyl alcohol and ultrasonication-assisted peeling method, which are compounded with aramid nanofibers (ANF) prepared by chemical dissociation, respectively, and the (BNNS/ANF)-(AgNWs/ANF) thermal conductivity and electromagnetic interference shielding composite films with Janus structures are prepared by the “vacuum-assisted filtration and hot-pressing” method. Janus (BNNS/ANF)-(AgNWs/ANF) composite films exhibit “one side insulating, one side conducting” performance, the surface resistivity of the BNNS/ANF surface is 4.7 × 10
13
Ω, while the conductivity of the AgNWs/ANF surface is 5,275 S/cm. And Janus (BNNS/ANF)-(AgNWs/ANF) composite film with thickness of 95 µm has a high in-plane thermal conductivity coefficient of 8.12 W/(m·K) and superior electromagnetic interference shielding effectiveness of 70 dB. The obtained composite film also has excellent tensile strength of 122.9 MPa and tensile modulus and 2.7 GPa. It also has good temperature-voltage response characteristics (high Joule heating temperature at low supply voltage (5 V, 215.0 °C), fast response time (10 s)), excellent electrical stability and reliability (stable and constant real-time relative resistance under up to 300 cycles and 1,500 s of tensile-bending fatigue work tests).
We investigate the microscopic mechanisms of ultralow lattice thermal conductivity (κl) in Tl3VSe4 by combining a first principles density functional theory based framework of anharmonic lattice ...dynamics with the Peierls-Boltzmann transport equation for phonons. We include contributions of the three- and four-phonon scattering processes to the phonon lifetimes as well as the temperature dependent anharmonic renormalization of phonon energies arising from an unusually strong quartic anharmonicity in Tl3VSe4. In contrast to a recent report by Mukhopadhyay et al. Science 360, 1455 (2018) which suggested that a significant contribution to κl arises from random walks among uncorrelated oscillators, we show that particlelike propagation of phonon excitations can successfully explain the experimentally observed ultralow κl. Our findings are further supported by explicit calculations of the off-diagonal terms of the heat current operator, which are found to be small and indicate that wavelike tunneling of heat carrying vibrations is of minor importance. Our results (i) resolve the discrepancy between the theoretical and experimental κl, (ii) offer new insights into the minimum κl achievable in Tl3VSe4, and (iii) highlight the importance of high order anharmonicity in low-κl systems. The methodology demonstrated here may be used to resolve the discrepancies between the experimentally measured and the theoretically calculated κl in skutterides and perovskites, as well as to understand the glasslike κl in complex crystals with strong anharmonicity, leading towards the goal of rational design of new materials.
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